Data storage devices of the type known as “Winchester” disc drives are well known in the industry. These disc drives magnetically record digital data on several circular, concentric data tracks on the surfaces of one or more rigid discs. The discs are typically mounted for rotation on the hub of a spindle motor. The spindle motor is mounted to a base deck. In disc drives of the current generation, the discs are rotated at speeds of more than 10,000 revolutions per minute.
Data are recorded to and retrieved from the discs by an array of vertically aligned read/write head assemblies, or heads, which are controllably positioned by an actuator assembly. Each head typically includes electromagnetic transducer read and write elements which are carried on an air bearing slider. The slider acts in a cooperative hydrodynamic relationship with a thin layer of air dragged along by the spinning discs to fly each head in a closely spaced relationship to the disc surface. In order to maintain the proper flying relationship between the heads and the discs, the heads are attached to and supported by flexures (also called head suspensions).
A typical disc drive has an actuator assembly with more than one arm supporting a number of flexure assemblies. Any structure, such as an actuator assembly, that has several identical components can have balanced modes of vibration. A balanced mode of vibration occurs for a structure when there is no net reaction force on the structure. Because balanced modes do not have a net reaction force acting on the structure, the vibration decay rate is determined solely by the individual identical components making up the structure.
When the vibration modes of the individual components are separated in frequency and when the remainder of the structure has high damping, then there is a greater degree of damping than what is caused by each individual component. The vibration modes of the individual components can be separated in frequency by making structural changes to eliminate the balanced modes.
When the vibration modes of the individual components, such as the flexure assemblies, are close in frequency, the excitation of one of the flexure assemblies can couple to produce sympathetic motion in one of the other flexure assemblies. If this occurs, the amplitude of vibration becomes higher than it would be for only one flexure assembly. This increase in the amplitude of vibration can cause an increase in the track following error and the position error that affects the reading and writing performance. Depending on the vibration mode, the increase in the amplitude of vibration could also cause head-to-disk contact. Thus, it is highly desirable to cause the flexure assemblies to have different resonant frequencies.
One method for separating vibration modes of the individual components is to make each flexure slightly different. U.S. Pat. No. 5,953,180 issued to Frater et al. (Frater '180) presents several alternative means of differentiating head/gimbal assemblies that share a common actuator arm. Each head/gimbal assembly is made up of a flexure, a gimbal, a head, and the slider for the head. If there is sufficient damping, these alternatives that Frater '180 disclose can be effective. However, providing different head/gimbal assemblies for each actuator arm can be relatively expensive and difficult to manage in a high volume manufacturing environment.
Thus, there is a need for an improved actuator assembly that overcomes these and other limitations of the prior art.